We wish to collect enough x-ray data on the nitrogenase MoFe proteins to sort out what metal centers are present and how they are organized with respect to each other. The first two major goals, getting stable crystals and having them diffract well, have been accomplished; the next major goal, getting heavy metal derivatives for obtaining the 3-dimensional structure, will be a primary goal next year. The identification of the FeS protein(s) from N2-fixing cells that donate FeS centers to apoproteins will be another primary goal. We will determine if any of these FeS proteins (other than the known nitrogenase proteins) are absent in cells grown on amonia or are present only in low concentration. Once isolated this FeS protein(s) will be characterized and examined in an vitro system for the ability to transfer FeS centers to apoproteins. Another primary goal is to determine the function of ATP hydrolysis in nitrogen fixation. This will be probed by the use of 18O to determine whether a phosphorylation is involved as well as by studies to determine the sites where ATP reacts. Since ATP binds to the Fe protein of nitrogenase without being hydrolyzed, studies will have to be made with the combined nitrogenase system.